1. Field of the Invention
The present invention relates to a yoke assembly and a method in accordance with the preambles of appended base claims for connecting and securing the rolls of an extended-nip press to each other.
2. Description of Background Art
Generally the press zone, or nip, in an extended-nip press is formed by two substantially parallel to each other aligned rolls that in the present case are a shoe roll and a backing roll. The shoe roll comprises a rotating endless-loop blanket of a flexible, liquid-impervious material, a rigid roll support beam mounted in a stationary fashion so as to extend axially through the interior of the endless blanket, at least one loading shoe supported by the support beam and having a concave top face, and loading means for pressing the concave top face of the loading shoe against the flexible endless blanket so that the endless blanket forms a press nip zone in cooperation with the backing roll. Both the shoe roll and the backing roll are rotatably mounted by their both ends in bearing blocks.
An extended-nip press is characterized by a high line load in the nip. At its maximum, the line load may be as high as 2000 kN/m. Hence, a conventional screw-loaded connection between the rolls is not generally practicable. Therefore, it is known in the art to adapt the bearing blocks of one roll in a close vicinity of the bearing blocks of the opposed roll so that the rolls may be connected and secured to each other by means of connecting members linking the bearing blocks to each other.
E.g., patent publication FI 101633 discloses a yoke assembly and method for connecting the rolls of an extended-nip press to each other. In the arrangement of cited patent publication, the bearing blocks of the extended-nip press rolls are joined to each other by connecting members. The connecting member described in the publication is adapted to rotate relative to the bearing block so that the end of the connecting member is locked in a wedged fashion to the other bearing block. The displacement, or outdistancing, of the connecting member from the bearing block, whereto the connecting member is joined, is effected by means of a hydraulic cylinder. In the construction according to cited publication, both roll ends are provided with two connecting members that are lockable to either side of the bearing block relative to the cross-machine center axis of the press rolls.
Both ends of the connecting member are provided with a pivot point allowing the connecting member to rotate pivotally in either one of the bearing blocks, whereby it is possible to select the upper or, alternatively, the lower bearing block to act as the pivot point. This construction suffers from several shortcomings including a need for wide elbowroom and incompatibility with the renovation requirements of existing machines.
Also patent publication U.S. Pat. No. 5,547,547 discloses an interconnection assembly for the rolls of an extended-nip press based on connecting members that are clampable to the bearing blocks. The roll interconnection arrangement described in cited publication comprises U-shaped connecting members that engage with the mating surfaces of the bearing blocks of the rolls. Additionally, each one of the connecting members is provided with pivot points about which the connecting member can be rotated to disengage from and engage with a mating surface provided on the bearing block. As described in cited publication, at both ends of the connecting members of the assembly is also adapted a hydraulic actuator having the end portions of the connecting members connected to its ends, whereby the hydraulic actuator facilitates the rotation of the connecting members about their pivot points. Inasmuch the arrangement of cited publication employs separate pivot points for implementing the rotation of the connecting members, the construction suffers from the need for wide elbowroom when the assembly is being disengaged. Furthermore, this embodiment is very critical as to its manufacturing tolerances in regard to trouble-free operation. Moreover, the roll nip must be initially driven quite wide to allow unrestricted opening of the press.